The overall objective is to study the interface of the placenta with its environment, in particular the nature and formation of the surface coats of the syncytial trophoblast, the cell biology of the synthesis of these coats, and the localized variation in properties of these coats with regard to protein binding. Cell coat synthesis will be studied using in vitro exposure of human placental villi to tritiated sugars and in certain cases to sugar nucleotides. The effects of prior enzyme digestion on the in vitro binding of protein tracers will also be studied.